Sewage pumping system



Aug. 9, 1966 F. s. was 3,265,009

' SEWAGE PUMPING SYSTEM Filed Aug. 7, 1963 2 Sheets-Sheet 1 1 42 92 INVENTOR.

United States Patent 3,265,009 SEWAGE PUMPING SYSTEM Frank G. Weis, Kansas City, Mo., assignor to Union Tank Car Company, a corporation of New Jersey Filed Aug. 7, 1963, Ser. No. 300,526 13 Claims. (Cl. 103235) This invention relates to sewage pumping systems employing reversible compressors, and more in particular to an improved, balanced rotor gas compressor constructed to reduce or prevent breakage of vanes.

It is frequently advantageous for a compressor and its driving motor to be mounted so that their axes of rotation are coincident. This enables the use of a single shaft for boththe motor and the compressor and elim inates the need for coupling drives such as pulleys and belts.

The usual type of compressor that has been mounted coaxially with its driving motor has a rotor offset from the center of the rotor housing or the rotor has an odd number of vanes. This causes the forces acting on different areas of the rotor to be unequal, and results in what is known as an unbalanced rotor design. When the compressor is to be used to pump a relatively large volume of gas, as for example more than 6 to 8 cubic feet per minute at or above about p.s.i., the forces on an unbalanced rotor type compressor prevent its being used in the coaxial motor-compressor combination described above. The reason is that the forces of unbalance on the rotor cause bending of the shaft connecting the rotor and motor. Deflection of the shaft causes the rotor to bind against the sides of the rotor housing, and this is obviously harmful.

To eliminate the above difliculty, a coaxial motor-compressor unit should employ a compressor of the type in which the rotor has an even number of vanes and the rotor is mounted in the center of a generally oval or elliptical housing having diametrically opposed discharge ports and diametrically opposed intake ports. In this arrangement the forces acting on different areas of the rotor are essentially equal so the rotor can be regarded as balanced. Such compressors can have a relatively tall rotor without the dangers of shaft deflection inherent in unbalanced rotor units.

The use of the above described balanced rotor compressors in systems in which solids or liquids are carried by the gas being compressed has not been wide spread in the past because the rotor vanes are frequently broken. Such vanes are ordinarily made from a carboniferous material because such materials are self-lubricating and thus have a relatively long life even though the vanes continually wear against the inside of the rotor housing. However, such materials are relatively frangible, and condensed vapors or other liquids, and solid particles entering the rotor housing shear ofl the ends of the vanes when such particles are compressed in the areas of minimum clearance between the rotor and its housing. The reason for this is that heretofore it was believed that the efficiency of such compressors would be reduced below an acceptable value if the total diametrical spacing between the rotor and the housing in the area of the minor axis of the elliptical cavity was greater than about .005 inch. This invention is based in part on the discovery that the minimum spacing between the rotor and its housing can be increased to a much greater magnitude without loss of efficiency and without breakage of vanes, provided that the spacing is held within certain critical limits.

Accordingly, it is an object of the invention to provide an improved gas compressor eliminating or at least reducing vane breakage caused by liquids or solids being entrained in the gas being compressed.

Another object is to provide an improved gas compres sor of normal to increased efiiciency in which vane breakage is reduced.

A further object is to provide a balanced-rotor gas compressor employing carboniferous vanes in which the spacing between the rotor and its housing is increased so as to reduce vane breakage caused by trapped liquids or solids, but without reducing the efliciency of the compressor.

A further object is to provide a sewage pumping system in which a balanced-rotor compressor pumps gas that has contacted sewage, but breakage of compressor vanes is reduced notwithstanding solid and liquid particles of sewage entering the compressor.

A further object is to provide an improved sewage pumping system employing a high capacity, relatively efficient gas compressor requiring little maintenance.

A further object is to provide an improved system employing a gas compressor to pump sewage in which shut down of the system to repair broken compressor vanes is minimized.

Other objects and advantages of the invention will be apparent from the drawing, specification, and claims, and the scope of the invention will be pointed out in the claims.

Briefly stated, according to one aspect of the invention, a reversible, balanced-rotor, gas compressor has a housing defining a generally elliptical cavity in which a gas intake port and a gas discharge port are located on opposite sides of the cavity adjacent the minor axis of the cavity, and a rotor is supported so that its axis is coincident with the center of the cavity. A plurality of diametrically opposed carboniferous vanes are slidable in radial slots of the rotor. The compressor can compress gases containing discrete amounts of liquid and solid matter without breaking the vanes and without loss of efficiency if the diameter of the rotor is from about .025 to about .085 inch less than the length of the minor axis of the cavity.

In the drawing:

FIG. 1 is a schematic, partially cross sectional view of an embodiment of the invention.

FIG. 2 is an enlarged cross sectional, partially broken away view taken along the line 2-2 in FIG. 1.

FIG. 3 is a cross sectional, partially broken away view on a reduced scale taken along the line 3-3 in FIG. 2.

FIG. 4 is a cross sectional, partially broken away view on a reduced scale taken along the line 4-4 in FIG. 2.

Referring to the drawing, FIG. 1 shows a system 9 for pumping sewage 10 in accord with the teachings of the invention. A sewage inlet \pipe 11 is connected adjacent the upper end of a sewage receiving chamber or tank 12, and a sewage outlet pipe 13 is connected adjacent the bottom of tank 12. A conventional check valve 14 in pipe 11 permits sewage to flow into tank 12 but not out of tank 12, and a similar check valve 15 in pipe 13 permits sewage to flow out of tank 12 but not into tank 12.

A combined motor compressor unit 17 for pumping sewage is attached to tank 12 by bolts 18. The unit 17 comprises a conventional reversible electric motor 21 connected to a suitable source of electric power and a gas compressor 22 in accord with the teachings of the invention. Compressor 22 communicates with the interior of tank 12 through a hole 23 so that it can withdraw air therefrom as sewage is flowing into tank 12 or compress air thereinto to eject the sewage.

When the system starts up, tank 12 is empty and compressor 22 runs in a direction that withdraws air therefrom. When the sewage level in tank 12 reaches a predetermined high level determined by a hollow, openended electrode 24, motor 21 is caused to reverse and thereby run compressor 22 in a direction that compresses air into tank 12. As air pressure builds up in tank 12, it forces the accumulated sewage out through pipe 13. When the sewage recedes to a predetermined low level determined by the electrodes 25 and 26, motor 21 stops. The electrodes 24-26 may be interconnected in any sewage ejector electrical control circuit 28 known to the art, it being understood that the specific details of such a circuit form no part of the present invention.

As shown in FIGS. 1 and 4, motor 21 is attached to compressor 22 by bolts 29 which pass through openings in lugs 30 on the compressor housing 31, and through openings in compressor lid 32; bolts 20 screw into tapped holes in the casing of motor 21. Housing 31 is attached to a base member 33 by bolts 34. The output shaft 35 of motor 21 passes through a hole in lid 32 and is coaxial with the center of an elliptical cavity 36 defined by the inside wall of housing 31.

A generally cylindrical rotor 37 is mounted for rotation in the center of cavity 36 by having its center axis coincident with shaft 35. Rotor 37 is secured to shaft 35 by a bolt 38 passing through its center and threading into a tapped hole in shaft 35.

A plurality of radial slots 40 are equally spaced around the periphery of rotor 37. A radially slidable vane 41 made from a carboniferous material such as resin treated electro graphite occupies each slot 40. As rotor 37 turns, centrifugal forces cause vanes 41 to move outwardly into contact with the inside surface of cavity 36 and thereby define chambers 43 of increasing or decreasing size for causing either pressure or suction at the ports in housing 31. For proper performance of the compressor and sewage pumping system, the number of slots 40 should be equal to 6n-4(n1), with n being a positive whole number. The preferred range for values of n is from 1 to 4, with 2 being the most preferred value for n. When 11:2, there will be 8 slots in the rotor, as shown in FIG. 2.

A first pair of diametrically opposed ports and 51 in housing 31 communicate with cavity 36. Ports 50 and 51 are interconnected through channels 52 and 53 and mating passages 54 and 55 in base member 33 with an opening 57, which communicates with the interior of tank 12. A second pair of diametrically opposed ports and 61 in housing 31. communicate with cavity 36. Ports 60 and 61 are interconnected through channels 62 and 63 and mating passages, such as 64 in base member 33, with an opening 66 which is vented to the atmosphere. For proper operation of the compressor, ports 50 and 60 on one side of cavity 36 and ports 51 and 61 on the other side of cavity 36 must be spaced far enough apart for at least one vane 41 to separate adjacent ports at all times. As shown in FIG. 4, ports 60 and 51 are staggered vertically; port 61 is at the same elevation as port 60, and port 50 is at the same elevation as port 51. This arrangement enables vanes 41 to wear more evenly than when all ports are at the same elevation, and thus increases the life of the vanes.

Turning of rotor 37 in a counter-clockwise direction causes compression at ports 50 and 51 and suction at ports 60 and 61; in this situation air is drawn in through opening 66, compressed in cavity 36, and then pumped through ports 60 and 61 and discharged through opening 57 into tank 12. Correspondingly, rotation of rotor 37 in a clockwise direction causes compression at ports 60 and 61 and suction at ports 50 and 51. This causes air to be withdrawn from tank 12 and pumped to the atmosphere.

Air drawn from tank 12 into cavity 36 frequently contains liquid and solid particles of sewage as well as moisture vapor. Compression of such air in elliptical cavity 36 causes deleterious accumulations of solid and liquid matter in the area adjacent the minor axis 68 of the cavity. To prevent breakage of vanes 41 resulting from their impact with such accumulations, the radial spaces 70 between housing 31 and rotor 37 can be increased to values which were heretofore considered unacceptable. It has been discovered that when the difference in length between the minor axis 68 and the diameter of rotor 37 (i.e., twice the radial spacing 70) is from about .025 to about .085 inch, vanes 41 are not broken by solids and liquids accumulating in cavity 36, and the efiiciency of the compressor remains at an unexpectedly high level. The preferred range of such diametrical differences in length is from about .050 to about .085 inch, with the preferred value being about .065 inch.

Tests were run to determine the effect on compressor efficiency of increasing the spacing between rotor 37 and its housing 31. A gas compressor of the same general structure as is shown in the drawing had a cylindrical rotor 4.981 inches in height contained in an elliptical cavity in a housing 5.001 inches in height; eight vanes 4.996 inches long made from Speer Carbon Co. Grade 9116 Graphite were slidable in slots uniformly spaced around the rotor. The length of the minor axis of the cavity was 3.058 inches, and the rotor was initially 3.053 inches in diameter, thus leaving a minimum total spacing of .005 between the rotor and the wall of the housing at the minor axis of the cavity. The inlet and outlet ports on each side of the housing adjacent the minor axis were 1 /2 inches apart at their closest edges.

The compressor .was run at a constant speed of 1750 r.p.m., first at an outlet pressure of 6 p.s.i., and then at an outlet pressure of 10 p.s.i., and its efiiciency was determined in the manner described below. Thereafter, the rotor was removed and its diameter was machined down to various smaller sizes, and the efliciency tests were repeated under the same conditions.

The efficiency of a compressor is its output horsepower divided by the electrical input horsepower, which was measured by wattmeter. It can be shown that for isentropic compression, compressor output horsepower is equal to:

P2 (0.283) ih-all 1 64.85

where:

Q=output volume of gas flow in cubic feet per minute, P =inlet pressure in pounds per square inch, P =outlet pressure in pounds per square inch,

Q was measured by placing an orifice plate across the discharge outlet of the compressor in accord with ASME Power Test Code for Displacement Compressors, Blowers, and Vacuum Pumps PTC 9-1954. All pressures were measured with a mercury manometer, with inlet pressure being atmospheric pressure at all times, and outlet pressure being kept constant by a throttling valve at the compressor outlet. Ambient temperature was essentially constant at about 72 F.

The results of the efficiency test for each spacing be- 5 tween the rotor and housing at the minor axis of the cavity are presented in the table below:

TABLE Q Electrical Spacing (Compressor Output Input Efiiciency (inches) 1 Output (Horse- (Horse- (Percent) Capacity in power) power) c.f.m.)

At 6 psi. Outlet Pressure At 10 p.s.i. Outlet Pressure 1 Minor axis 68 of elliptical cavity 36 minus diameter of rotor 37.

The table shows that contrary to expectation, the efiiciency of the compressor did not drop sharply as the spacings 70 bet-ween rotor 37 and housing 31 were increased above the prior art maximum of about .005 inch. On the contrary, compressor efiiciency rose slightly until maximum efliciency was reached at a spacing of about .065 inch. Efiiciency did not drop sharply below that found for the .005 inch spacing until the spacing was increased above about .085 inch.

The tests described above were expected to show that compressor efiiciency drops sharply as the spacing 70 was increased. The discovery that compressor efliciency did not drop sharply in the spacing range between about .0- and about .085 inch was highly unexpected. This has the efiect of permitting the spacings 70 to be increased to a value at which vanes 4-1 will not be broken with no less of compressor effioiency. Subsequent tests have shown that when a compressor constructed as described herein was run under field conditions in a sewage ejector, vanes 41 did not break; the spacing between the rotor and its housing was .065 inch. Under essentially the same field conditions, vane breakage had been a severe problem with spacings of about .005 inch.

Turning now to FIGS. 1 and 3, hollow electrode 24 is shown connected to compressor 22. by a unitary insulatornozzle element 80, which is made from a suitable corrosion resistant electrical insulating material, such as polyethylene. Threaded end 81, which has a first opening 82, screws into opening 57 in base 33, and the closed end of electrode :24 is secured by any suitable means in a second opening 83 at the other end of the element 80. Openings 82 and 83 are connected by a first passage 84. An insulated electrical conductor 85 is soldered to electrode 24 at 86. Conductor 85 passes through first passage 84, opening 57, passage 55 in base 33, and finally out through an opening 88, and is then connected into motor control circuit 28.

One or more air discharging nozzles 89 are defined by second passages 90 which intersect first passage '84. Nozzles 89 project outwardly from element 80, and their discharge ports 91 are oriented to expel air from compressor 22 upwardly toward the top of tank 12 and away from electrode 2 4. When compressor 22 is evacuating tank 12, nozzles 89 d-raw air into compressor 22 from adjacent the top of tank 12 and thus reduce the amount of solid and liquid material drawn into the compressor. A drain hole 92 may be provided in the closed end of hollow electrode 24 to enable moisture that condenses in compressor 22 or element 80 to drain through the open end of the electrode into tank '12. The drain 92 should be small enough to 6 prevent any significant amount of air from being discharged therethrough.

Heretofore, in sewage ejectors the practice has been to force air through a nozzle or a hollow electrode that expels the air downwardly towards the sewage. This caused splashing of sewage upwardly onto electrode 24 when the sewage is at or near its highest level. The result was that electrode 24 often became so covered with crud that it was rendered inoperative with a consequent failure of the sewage pumping system. The combined insulator-nozzle element solves this problem by expelling air in a direction that prevents splashing of sewage.

It will be understood that while the form of the inven tion herein shown and described constitutes a preferred embodiment, it is not intended herein to illustrate all of the equivalent forms or ramifications thereof. It will also be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed, and it is aimed in the appended claims to cover all such changes as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a reversible, balanced rotor, gas compressor having:

(1) a housing defining an elliptical cavity having a minor axis of predetermined length,

(2) there being a gas intake port and a gas discharge port in opposite sides of said housing in the area adjacent said minor axis,

(3) a circular rotor supported rotatably in said housing so that its axis is coincident with the center of said elliptical cavity, said rotor having a diameter of predetermined length,

(4) there being an even number of slots in said rotor,

(5) a breakable vane slidable in each slot, and

(6) said slots and said ports being oriented so that a vane is always located between the intake port and discharge port on the same side of said housing;

the improvement enabling said compressor to efficiently compress gases containing discrete amounts of liquid and solid matter without breaking said vanes comprising:

said length of said rotor diameter being from about .025 to about .085 inch less than said length of said minor axis.

2. The invention of claim 1 wherein said length of said rotor diameter is from about .050 to about .085 inch less than said length of said minor axis.

3. The invention of claim 2 wherein said length of said rotor diameter is about .065 inch less than said length of said minor axis.

4. The invention of claim 1 wherein the number of slots in said rotor is equal to 6n4(n1), with n being a positive whole number.

5. The invention of claim 4 wherein n is from 1 to 4.

6. The invention of claim 6 wherein 11:2.

7. A sewage pumping system comprising:

(1) chamber means into which sewage is drawn as air is expelled therefrom and then from which sewage is ejected by the pressure of air being compressed thereinto, said air containing condensible moisture vapor and solid particles from said sewage as it comes from said chamber means, and

(2) a balanced rotor, reversible, motor-compressor unit for withdrawing from said chamber or compressing thereinto at least six cubic feet per minute of air, comprising:

(a) a reversible motor having shaft means coaxially aligned with and directly coupled to a generally circular rotor at the center thereof, said rotor having a diameter of predetermined length,

(b) wall means defining a generally elliptical cavity receiving said rotor, said elliptical cavity having a minor axis of predetermined length,

(c) the central axis of said rotor being aligned with the center of said cavity,

((1) said rot-or having radial slots receiving slidable vanes made from a material breakable by condensed moisture and solid particles of sewage trapped between said rotor and said wall means, and

(e) said length of said rotor diameter being from about .025 to about .085 inch less than said length of said minor axis, whereby suflicient clearance is provided to permit passage of said condensed moisture and solid particles between said rotor and said wall without breaking said vanes.

8. The invention of claim 7 wherein said length of said rotor diameter is from about .050 to about .085 inch less than said length of said minor axis.

9. The invention of claim 8 wherein said length of said rotor diameter is about .065 inch less than said length of said minor axis.

10. A sewage pumping system comprising:

(1) chamber means into which sewage is drawn as air is expelled therefrom and then from which sewage is ejected by the pressure of air being compressed thereinto, said air containing condensible moisture vapor and solid particles from said sewage as it passes from said chamber means, and

(2) a balanced rotor, reversible, motor-compressor unit for withdrawing from said chamber or compressing thereinto at least six cubic feet per minute of air, comprising:

(a) a reversible motor having shaft means coaxially aligned with and directly coupled to a generally circular rotor at the center thereof, said rotor having a diameter of predetermined length,

(b) a housing defining a generally elliptical cavity receiving said rotor, said elliptical cavity having a minor axis of predetermined length,

(c) the central axis of said rotor being aligned with the center of said cavity,

(d) there being a gas intake port and a gas discharge port in opposite sides of said housing in the area adjacent said minor axis, the intake ports being diametrically opposed to each other and the discharge ports being diametrically opposed to each other,

(e) said rotor having an even number of radial slots receiving slidable vanes made from a material breakable by condensed moisture and solid particles of sewage trapped between said rotor and said housing,

(f) said slots and ports being oriented so that a vane is always located between the intake port and the discharge port on the same side of said housing, and

(g) said length of said rotor diameter being from about .025 to about .085 inch less than said length of said minor axis, whereby suflicient clearance is provided to permit passage of said condensed vapors and solids between said rotor housing wall without breaking said vanes.

11. In a combined motor-compressor unit having:

(1) a reversible electric motor including an output shaft, and

(2) a balanced rotor gas compressor having:-

(a) a housing defining an elliptical cavity, said elliptical cavity having a minor axis of predetermined length,

(b) there being a gas intake port and a gas dis charge port in opposite sides of said housing in the area adjacent the minor axis of said elliptical cavity, the intake ports being diametrically opposed to each other and the discharge ports :being diametrically opposed to each other,

(0) a circular rotor supported rotatably in said housing so that its axis is coincident with the center of said elliptical cavity, said rotor having a diameter of predetermined length,

(d) said motor output shaft being coaxially aligned with and directly secured to said rotor,

(e) said rotor having radial slots in which are slidable vanes made from a material breakable by condensed moisture and solid particles compressed in said cavity, and

(f) said length of said rotor diameter being from' about .025 to about .085 inch less than said length of said minor axis, whereby sufiicient clearance is provided to permit passage of said condensed vapors and solids between said rotor and cavity wall without breaking said vanes.

12. In a combined motor-compressor unit having:

(1) a reversible electric motor including an output shaft, and

(2) a balanced rotor gas compressor having:

(a) a housing defining an elliptical cavity, said elliptical cavity having a minor axis of predetermined length,

(b) there being a gas intake port and a gas discharge port in opposite sides of said housing in the area adjacent the minor axis of said elliptical cavity, the intake ports being diametrically opposed to each other and the discharge ports being diametrically opposed to each other,

(c) a lid bolted'to the upper end of said housing for closing one end of said cavity,

(d) said housing being bolted to a supporting base member at its other end,

(e) a circular rotor supported rotatably in said housing so that its axis is coincident with the center of said elliptical cavity, said rotor having a diameter of predetermined length,

(f) said motor output shaft passing through a hole in said lid and being coaxially aligned with and connected to said rotor by a coaxial bolt passing through the center of said rotor and screwing into said shaft,

(g) said rotor having radial slots in which are slidable vanes made from a material breakable by condensed moisture and solid particles compressed in said cavity, and

(h) said length of said rotor diameter being from about .025 to about .085 inch less than said length of said minor axis, whereby sufiicient clearance is provided to permit passage of said condensed vapors and solids between said rotor and cavity wall without breaking said vanes.

13. In a reversible, balanced rotor, gas compressor comprising:

(1) a housing defining an elliptical cavity, said elliptical cavity having a minor axis of predetermined length,

(2) there being a gas intake port and a gas discharge port in opposite sides of said housing in the area adjacent the minor axis of said elliptical cavity,

(a) the intake ports being diametrically opposed to each other and the discharge ports being diametrically opposed to each other,

(b) the intake ports and discharge ports respectively being staggered axially with relation .to each. other,

(3) a circular rotor supported rotatably in said housing so that its axis is coincident with the center of said elliptical cavity, said rotor having a diameter of predetermined length,

(4) there being an even number of diametrically 0pposcd radial slots in said rotor,

9 (5) a radially slida-ble carboniferous vane in each slot,

and (6) said slots and said ports being oriented so that a vane is always located between the intake port and discharge port on the same side of said housing; the improvement enabling said compressor to efiiciently compress gases containing discrete amounts of liquid and solid matter Without breaking said vanes comprising:

said length of said rotor diameter being from about .025 to about .085 inch less than said length of said minor axis.

References Cited by the Examiner UNITED STATES PATENTS 745,755 12/1903 Allen 230-153 813,018 2/1906 Okun 123-16 991,314 5/1911 Humphreys 230-153 1,994,454 3/1935 Cross 23927 2,180,274 11/1939 Bentley 103-235 2,266,205 12/ 1941 Hunter 103-25 2,385,905 10/1945 Yeomans 103-234 2,416,980 3/ 1947 Burns 103-3 2,434,027 1/ 1948 WhittingtOn 103-235 2,711,698 6/1955 Bozek et a1 103-136 MARK NEWMAN, Primary Examiner. 20 LAURENCE V. EFNER, DONLEY J. STOCKING,

Examiners.

G. M. THOMAS, W. J. KRAUSS,

Assistant Examiners. 

1. IN A REVERSIBLE, BALANCED ROTOR, GAS COMPRESSOR HAVING: (1) A HOUSING DEFINING AN ELLIPTICAL CAVITY HAVING A MINOR AXIS OF PREDETERMINED LENGTH, (2) THERE BEING A GAS INTAKE PORT AND A GAS DISCHARGE PORT IN OPPOSITE SIDES OF SAID HOUSING IN THE AREA ADJACENT SAID MINOR AXIS, (3) A CIRCULAR ROTOR SUPPORTED ROTATABLY IN SAID HOUSING SO THAT IT AXS IS COINCIDENT WITH THE CENTER OF SAID ELLIPTICAL CAVITY, SAID ROTOR HAVING A DIAMETER OF PREDETERMINED LENGTH, (4) THERE BEING AN EVEN NUMBER OF SLOTS IN SAID ROTOR, (5) A BREAKABLE VANE SLIDABLE IN EACH SLOT, AND (6) SAID SLOTS AND SAID PORTS BEING ORIENTED SO THAT A VANE IS ALWAYS LOCATED BETWEEN THE INTAKE PORT AND DISCHARGE PORT ON THE SAME SIDE OF SAID HOUSING; 